Variable Message lenght GSV, add field GNSS Signal ID

Any Way to add support for variable Message lenght?

When refering to the ublox ZED-F9P Manual Chapter 4.2.14 'GSV', the GSV has variable message lenght. Does look like NMEA 4.10 not proprietary.

An example GSV Output Set from this module

$GPGSV,3,1,11,04,06,317,21,05,17,057,34,09,00,348,,12,01,118,,1*68
$GPGSV,3,2,11,16,17,300,17,18,57,162,38,21,57,173,37,25,29,121,33,1*6A
$GPGSV,3,3,11,26,49,301,08,29,58,056,37,31,50,235,22,1*55

The 3rd Message is interpreted as

<GSV(num_messages='3', msg_num='3', num_sv_in_view='11', sv_prn_num_1='26', elevation_deg_1='49', azimuth_1='301', snr_1='21', sv_prn_num_2='29', elevation_deg_2='58', azimuth_2='056', snr_2='36', sv_prn_num_3='31', elevation_deg_3='50', azimuth_3='235', snr_3='23', sv_prn_num_4='1')>

But the '1' just before checksum (Pos 16, 12 respectively) is supposed to be GNSS Signal ID instead of sv_prn_num_4='1'

Hi,

I implemented some sort of fix to this in https://github.com/Knio/pynmea2/pull/115 (described there in more detail). Also available in the master branch of my fork.

You can see that using the GSV_signal_id=True removes the erroneus key sv_prn_num_# and adds signal_id.

Example 1

In [1]: pynmea2.parse("$GPGSV,3,3,09,25,,,40,1*6E")
Out[1]: <GSV(num_messages='3', msg_num='3', num_sv_in_view='09', sv_prn_num_1='25', elevation_deg_1='', azimuth_1='', snr_1='40', sv_prn_num_2='1')>

In [2]: pynmea2.parse("$GPGSV,3,3,09,25,,,40,1*6E", GSV_signal_id=True)
Out[2]: <GSV(num_messages='3', msg_num='3', num_sv_in_view='09', sv_prn_num_1='25', elevation_deg_1='', azimuth_1='', snr_1='40', signal_id='1')>

Example 2

In [1]: pynmea2.parse("$GPGSV,3,3,11,26,49,301,08,29,58,056,37,31,50,235,22,1*55")
Out[1]: <GSV(num_messages='3', msg_num='3', num_sv_in_view='11', sv_prn_num_1='26', elevation_deg_1='49', azimuth_1='301', snr_1='08', sv_prn_num_2='29', elevation_deg_2='58', azimuth_2='056', snr_2='37', sv_prn_num_3='31', elevation_deg_3='50', azimuth_3='235', snr_3='22', sv_prn_num_4='1')>

In [2]: pynmea2.parse("$GPGSV,3,3,11,26,49,301,08,29,58,056,37,31,50,235,22,1*55", GSV_signal_id=True)
Out[2]: <GSV(num_messages='3', msg_num='3', num_sv_in_view='11', sv_prn_num_1='26', elevation_deg_1='49', azimuth_1='301', snr_1='08', sv_prn_num_2='29', elevation_deg_2='58', azimuth_2='056', snr_2='37', sv_prn_num_3='31', elevation_deg_3='50', azimuth_3='235', snr_3='22', signal_id='1')>

Example 3

In [1]: pynmea2.parse('$GAGSV,1,1,00,2*76\r\n')
Out[1]: <GSV(num_messages='1', msg_num='1', num_sv_in_view='00', sv_prn_num_1='2')>

In [2]: pynmea2.parse('$GAGSV,1,1,00,2*76\r\n', GSV_signal_id=True)
Out[2]: <GSV(num_messages='1', msg_num='1', num_sv_in_view='00', signal_id='2')>

Knio / pynmea2